36.1 Features
Retinitis pigmentosa (RP) is a group of genetically and phenotypically heterogeneous conditions affecting approximately 1 in 4,000 individuals. RP can be inherited in an autosomal dominant (15–25%), autosomal recessive (5–20%), or X-linked (5–15%) manner. To date, 22 genes have been identified to cause dominant RP, 39 genes identified to cause recessive RP, and 2 genes identified to cause X-linked RP. There are also numerous syndromic forms of RP, such as Usher and Bardet–Biedl syndromes. RP is characterized by degeneration of rod and cone photoreceptor cells. Sector RP is an atypical form of RP which involves only one or two quadrants of the retina showing clinical signs of the disease (pigmentary changes and visual field loss). It is usually characterized by bilateral symmetrical retinal degeneration in the inferior nasal quadrant. The majority of sector RP cases are the result of mutations in the RHO gene.
Fig. 36.1 Optical coherence tomography in retinitis pigmentosa demonstrating perifoveal ellipsoid zone and outer nuclear loss. Foveal preservation is seen.
36.1.1 Common Symptoms
Symptoms and age of onset may be highly variable. Nyctalopia and constriction of visual field are usually the initial symptoms, with diminished color vision and central vision loss over time due to affected cone photoreceptor cells. Loss of light perception may be observed in severe cases.
36.1.2 Exam Findings
Optic nerve pallor, attenuated vessels, bone spicules in mid and far peripheral retina, vitreous cells, and posterior subcapsular lens opacities may be present (▶ Fig. 36.2).
Fig. 36.2 Ultra-widefield photography of retinitis pigmentosa with 360-degree bone spicule pigmentation, optic nerve pallor, and vessel attenuation.
36.2 Key Diagnostic Tests and Findings
36.2.1 Optical Coherence Tomography
Progressive reduction in the total thickness of various outer retinal structures is seen on optical coherence tomography (OCT). In fact, ellipsoid zone bandwidth has been proposed as a tool to monitor disease progression. Foveal preservation is often seen, particularly early in the disease, with outer retinal loss in the surrounding retina (▶ Fig. 36.1). Occasionally, cystoid macular edema may be present.
36.2.2 Fundus Autofluorescence
Hypoautofluorescent areas corresponding to the areas of outer retinal atrophy are seen. In the macular region, a perifoveal hyperautofluorescent ring has been proposed to serve as an indicator of prognosis with posterior migration of the ring indicating progression of the disease (▶ Fig. 36.3). The sectoral distribution of sectoral RP may also be demonstrated by fundus autofluorescence (FAF; ▶ Fig. 36.4).
Fig. 36.3 Ultra-widefield fundus autofluorescence image in retinitis pigmentosa exhibiting hyperfluorescent macular ring.
Fig. 36.4 Ultra-widefield fundus autofluorescence image with sector retinitis pigmentosa.
36.2.3 Visual Field Testing
Kinetic and static visual field testing typically shows progressive scotomas in the mid periphery. As disease progresses, the small islands of vision remaining in the far peripheral field and in the visual axis slowly disappear (▶ Fig. 36.5).
Fig. 36.5 Visual field demonstrated peripheral vision loss in retinitis pigmentosa.
36.2.4 Electroretinography
Reduced rod and cone response amplitudes and a prolonged time interval to peak rod or cone responses are seen on full-field electroretinography (ffERG). Amplitudes of the a- and b-waves are either reduced or nondetectable.
36.2.5 Fundus Photography
Optic disc pallor, attenuated retinal arterioles, and peripheral intraretinal pigment deposits known as bone spicules are observed.
36.2.6 Genetic Testing
Multiple clinical laboratories offer testing, though labs may vary in methodology, genes tested, interpretation of results/style of test reports, cost, and turn-around time. Positive genetic test results may allow for recurrence risk counseling, testing of other family members, provision of prognostic information, and ability to participate in potential clinical trials such as gene therapy. Genetic testing should be obtained through a certified genetic counselor as comprehensive testing may yield incidental, inconclusive, and unexpected findings. Depending on the laboratory and testing methodology utilized, diagnostic genetic test results can be obtained in over 50% of patients.
36.3 Critical Work-up
RP may be characterized as nonsyndromic or syndromic. In syndromic RP, patients have RP as a feature due to an underlying systemic genetic syndrome (▶ Table 36.1). Thus, careful attention to medical history is crucial for making an accurate clinical diagnosis and ensuring proper medical management and patient referrals. Associated symptoms and conditions in ▶ Table 36.1 should be screened for at time of diagnosis. Much like nonsyndromic RP, the various types of syndromic RP exhibit significant genetic heterogeneity and variable expressivity.
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